Wolfgang Grandegger wrote:
On 10/18/2005 08:14 PM Philippe Gerum wrote:
Wolfgang Grandegger wrote:
On 10/18/2005 01:44 PM Philippe Gerum wrote:
Philippe Gerum wrote:
Wolfgang Grandegger wrote:
Hallo,
attached you will find the results of Xemonai latency measurements on
various embedded PowerPC boards using MPC 8xx and AMCC 4xx processors,
from low to high end covering a worst case latency range from 25 to 225
us. It also includes a comparison with RTAI 3.0r5 on the slowest CPU.
Here are some remarks and comments:
- On low-end processor code size matters a lot and it's difficult to
beat RTAI/RTHAL.
Beat no, get closer, yes, probably. The good news is that looking at the
figures, we do have a margin of improvement! :o>
Btw, the nucleus can be configured so that the user-space threading
engine is compiled out (i.e. CONFIG_XENO_OPT_PERVASIVE from the nucleus
menu), which would be the corresponding profile to compare with klatency
(i.e. sched_up). Disabling this option reduces the code size for the
nucleus from:
text data bss dec hex filename
66740 792 6540 74072 12158
nucleus/xeno_nucleus.ko
to:
text data bss dec hex filename
52596 576 3956 57128 df28
nucleus/xeno_nucleus.ko
Disabling the periodic timer support which is unused for the klatency test
brings this down to:
text data bss dec hex filename
51040 544 3956 55540 d8f4 nucleus/xeno_nucleus.ko
OK, here are the new figures with (*)
CONFIG_XENO_OPT_PERVASIVE is not set
CONFIG_XENO_HW_PERIODIC_TIMER is not set:
|-----lat min|-----lat avg|-----lat max|-overrun|---test-time
RTAI 3.0r5 | 23120| 31838| 70520| ?| 00:12:26
Xenomai | 50560| 98976| 199040| 0| 00:09:45
Xenomai (*)| 44160| 96215| 200640| 0| 00:09:53
The min latency decreases as expected.
I just discovered that -00 did not include some recent changes I had in my tree,
aimed at prevent high latencies during fork pressure. I've committed -01 which
does include them. When time allows, I'd be interested to know if this has some
impact on the Ocotea figures. TIA,
bash-2.05b# cat /proc/ipipe/version
1.0-01
SWITCH without load:
== Sampling period: 100 us
RTH| lat min| lat avg| lat max| lost
RTD| 5158| 5169| 10038| 0 iPipe 1.0-00
RTD| 5145| 5154| 10166| 0 iPipe 1.0-01
KLATENCY with load:
RTH|-----lat min|-----lat avg|-----lat max|-overrun|----lat best|---lat
worst
RTS| 2953| 5974| 19147| 0| 00:12:05 1.0-00
RTS| 3035| 8705| 20705| 0| 00:09:54 1.0-01
LATENCY with load:
== Sampling period: 100 us
RTH|-----lat min|-----lat avg|-----lat max|-overrun|----lat best|---lat
worst
RTS| 3575| 7438| 24474| 0| 00:10:50 1.0-00
RTS| 3553| 10125| 23970| 0| 00:09:41 1.0-01
Mmm, average even looks worse for both latency tests.
It has no significant impact, I think.
Ok, thanks. The same fix is worth 10 us on high-end x86 boxen, so I wondered if
the same could apply to ppc as well.
--
Philippe.
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